The Distal VH Gene Cluster of the Igh Locus Contains Distinct Regulatory Elements with Pax5 Transcription Factor-Dependent Activity in Pro-B Cells

Summary V H -DJ H recombination of the immunoglobulin heavy chain ( Igh ) locus is temporally and spatially controlled during early B cell development, and yet no regulatory elements other than the V H gene promoters have been identified throughout the entire V H gene cluster. Here, we discovered regulatory sequences that are interspersed in the distal V H gene region. These conserved repeat elements were characterized by the presence of Pax5 transcription factor-dependent active chromatin by binding of the regulators Pax5, E2A, CTCF, and Rad21, as well as by Pax5-dependent antisense transcription in pro-B cells. The P ax5- a ctivated i ntergenic r epeat (PAIR) elements were no longer bound by Pax5 in pre-B and B cells consistent with the loss of antisense transcription, whereas E2A and CTCF interacted with PAIR elements throughout early B cell development. The pro-B cell-specific and Pax5-dependent activity of the PAIR elements suggests that they are involved in the regulation of distal V H -DJ H recombination at the Igh locus.